1. Field of the Invention
The present invention is directed to an apparatus for controlled venting of gas and particulate contaminants from a gas assist injection mold. More specifically, the present invention is directed to a gas assist mold dump valve that utilizes a gas controller to regulate the venting of gas from the mold cavity.
2. Reference to Related Art
During gas assist injection molding, the gas used to pack out the mold cavity must be vented before the mold may be opened to remove the molded part. Typically, this venting is regulated by the same device that is used to pressurize the mold, i.e., a gas controller. As a result of this dual use, the gas controller is directly exposed to particulate matter and condensing gases that are emitted from the mold cavity following the packing process. These expelled contaminants will characteristically coat the system of tubing which connects the gas controller to the mold. Over time, contaminant build-up restricts the tubing and may cause a significant decrease in the functionality and efficiency in the operations of the controller. The controller is also susceptible to damage caused by the build-up of mold gas contaminants exposed to particulate matter and condensing gases emitted from the mold cavity.
A variety of methods are disclosed in the prior art to overcome these and other harmful effects of the backflow of particulate matter through the gas controller or the tubing connecting the controller to the mold. One method uses a check valve disposed within the tubing between the controller and the mold to vent the mold gases directly to the atmosphere or into a recycling system. In an alternative method, a mechanically opened valve is mounted on the mold inlet tubing downstream of the check valve.
While these prior art methods permit venting of the mold without backflow of contaminants through the gas controller, they have the disadvantage of isolating the mold cavity from the gas controller during the entire venting phase of production. More importantly, the gas controller no longer has the ability to control the venting of the mold cavity. Therefore, it would be advantageous to have a means of venting the mold cavity wherein a gas controller retains the ability to regulate venting operations without the need to pass contaminated mold gas back through the controller.